WATER SUPPLY
  DIVISION

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       CROSS-CONNECTION


       CONTROL  MANUAL
U.S. Environmental Protection Agency



       Office of Water Programs



         Water Supply Division



        First Printed 1973 Reprinted in 1974,1975



     For sale by the Superintendent of Documents, U.S. Government Printing Office
               Washington, D.C. 20402 - Price $1
           Stock No. 055-001-00614-4/Catalog No. EP 2.8:C88

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                               PREFACE

  Plumbing cross-connections,  which  connect potable  water  supply with
nonpotable supply, are  a public  health problem.  There are numerous and
well-documented cases where such  connections have  been responsible for
contaminated  drinking water, and have resulted in spread  of  disease. The
problem is a dynamic  one,  because piping systems are continually  being
installed, altered, or extended.
  Control  of cross-connections is  possible, but only through knowledge and
vigilance.  Education is essential, for  many  of those who are experienced in
piping installation  fail to recognize cross-connection possibilities and dangers.
All municipalities  with  public  water supplies  should have cross-connection
control programs.  Those  responsible for  institutional or semipublic  water
supplies also should be familiar with the dangers, and should exercise careful
surveillance.
  The Cross-Connection Control Manual has been designed as a tool for health
officials, waterworks personnel, plumbers, and many others; it is intended to
be  used in educational, administrative, and technical  ways in conducting
cross-connection control programs. This manual is a revision of an earlier book
entitled Water Supply and Plumbing  Cross-Connections (PHS Publication No.
957), which was produced under the direction of Floyd B. Taylor by Marvin T.
Skodje, who wrote  the text and designed the illustrations.
  This new edition contains many of the original illustrations and much of the
text.  Some figures  and all chapters have been clarified and updated and some
extraneous material has  been  omitted. The work was  done  by Peter C.
Karalekas,  Jr.,  with  guidance  from Roger D.  Lee; it also  incorporates
suggestions made by the staff  of the Water Supply Division, other  govern-
mental agencies, and interested individuals.
  Chapter  2, "Public Health Significance of Cross-Connections," appeared in
Modern Sanitation  and Building Maintenance, vol. 14, No. 7  (July 1962).
Permission to reprint  has been given. Also, more  recent examples of cross-
connection cases have been included at the end of chapter 2.
                                                                      ill

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                                 CONTENTS
                                                                            Page
            Preface    	     iii
            List of Illustrations   	     vi
            American Water Works Association Policy on Cross-Connections   .  .     vii



Chapter

    1        Purpose and Scope	     	      1
    2        Public Health Significance of Cross-Connections   	      3
    3        Theory of Backflow and Backsiphonage	      9
    4        Methods and Devices for Backflow Prevention	     19
    5        Testing Procedures for Backflow Preventers	     27
    6        Administration of a Cross-Connection Control Program   	     32
    7        Cross-Connection Control Ordinance Provisions   	     35



Appendixes

   A        Partial List of Plumbing Hazards	     43
    B        Illustrations of Backsiphonage	     44
    C        Illustrations of Backflow   	     48
   D        Illustrations of Airgaps   	     51
    E        Illustrations of Vacuum Breakers   	     52
    F        Glossary	     53
    G        Bibliography   	     55
   H        Sample Cross-Connection Survey Form  	     56

Index   	     57

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                             ILLUSTRATIONS

Figure                                                                       fhge
     1   Pressure exerted by 1 foot of water at sea level	     10
     2   Pressure exerted by 2 feet of water at sea level   	     11
     3   Pressure on the free surface of a liquid at sea level	     11
     4   Effect of evacuating air from a column  	     12
     5   Pressure relationships in a continuous fluid system at the same elevation- •     13
     6   Pressure relationships in a continuous fluid system at different elevations .     14
     7   Backsiphonage_in a plumbing system   	     15
     8   Negative pressures created by constricted flow   	     15
     9   Dynamically reduced pipe pressures    	     16
    10   Valved connection between potable water and nonpotable fluid   	     17
    11   Valved connection between potable water and sanitary sewer	     17
    12   Airgap on lavatory  	     19
    13   Surge tank and booster pump	     20
    14   Booster system   	     22
    15   Operation of a vacuum breaker   	     23
    16  ^Typical non-pressure-type vacuum breaker installation  	     24
    17   Reduced pressure zone backflow preventer — principle of operation   ...     25
    18   Pressure-type vacuum breaker installation	     28
    19   Reduced pressure zone backflow preventer field test  	     29
    20   Method of testing check valves   	     30
    21   Backsiphonage — case 1  	     44
    22   Backsiphonage — case 2	     45
    23   Backsiphonage — case 3	     46
    24   Backsiphonage — case 4	     47
    25   Backsiphonage — case 5	     47
    26   Backsiphonage — case 6	     48
    27   Backflow - case 1   	     48
    28   Backflow - case 2	     49
    29   Backflow - case 3	     50
    30   Backflow - case 4	     50
    31   Airgap to sewer subject to backpressure — force main   	     51
    32   Airgap to sewer subject to backpressure — gravity drain   	     51
    33   Fire system makeup tank for a dual water system	     52
    34   Vacuum breakers  	     52
    35   Vacuum breaker arrangement for an outside hose hydrant   	     53
VI

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                     American Water Works Association

                   POLICY ON CROSS-CONNECTIONS

         A statement adopted by Board of Directors on Jan. 26, 1970

  The American  Water Works Association recognizes that the water purveyor
has a  responsibility to provide  its customers at the service  connection with
water that is safe under all foreseeable circumstances. Thus, in the exercise of
this  responsibility  the water purveyor  must take reasonable precaution to
protect the community distribution system from the hazards originating on the
premises  of  its customers  that may  degrade the water in  the community
distribution system.
  It is  realized that  cross-connection control and  plumbing inspections  on
premises  of  its customers are regulatory in  nature and should be  handled
through the rules, regulations, and recommendations of the health authority or
the plumbing-code enforcing agencies having jurisdiction. The water purveyor,
however,  should  be  aware  of any  situation requiring  inspection and/or
re-inspections  necessary to  detect  hazardous  conditions  resulting  from
cross-connections.  If,  in  the  opinion  of the  utility,  effective  measures
consistent with the  degree  of hazard  have  not been taken by the regulatory
agency,  the  water purveyor  should  take  such  measures  as he may deem
necessary to  ensure that the community distribution system is protected from
contamination.  Such  action  would  include  the  installation of a backflow
prevention  device,  consistent  with  the  degree  of hazard,  at  the service
connection, or discontinuance of the service.
                                                                       vu

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                  Chapter 1.  PURPOSE AND SCOPE

  Public health officials have long been concerned about cross-connections and
backflow connections in plumbing systems and in public drinking water supply
distribution  systems.  Such  cross-connections,  which  make  possible the
contamination of potable water, are ever-present dangers. One example of what
can happen is an  epidemic that occurred in Chicago  in 1933. Old, defective,
and improperly  designed plumbing and fixtures permitted the contamination
of drinking water. As a result, 1,409 persons contracted amebic dysentery;
there were 98 deaths. This epidemic, and others resulting from contamination
introduced into a water supply through improper plumbing, made clear the
responsibility  of public  health  officials and  water purveyors for  exercising
control over public  water distribution systems and all plumbing  systems
connected to them. This responsibility  includes advising and  instructing
plumbing installers in the recognition and elimination of cross-connections.
  Cross-connections  are  the links  through which  it is  possible for
contaminating materials to enter  a potable water supply.  The contaminant
enters the potable water  system  when the pressure of the polluted source
exceeds  the  pressure of  the  potable source. The action may  be called
backsiphonage or backflow. Essentially it is a reversal of the hydraulic gradient
that can be produced by a variety of circumstances.
  It   might be  assumed  that  steps for  detecting  and  eliminating  cross-
connections  would  be  elementary  and obvious. Actually,  cross-connections
may  appear in  many subtle  forms and in unsuspected  places.  Reversal of
pressure in the water may be freakish and unpredictable. The probability of
contamination of drinking  water through a cross-connection occurring within a
single plumbing  system may seem remote; but, considering the  multitude of
similar systems, the probability is great.
  Why do such cross-connections exist?
  First, plumbing  is  frequently  installed by persons who  are unaware of the
inherent dangers of cross-connections. Second, such connections are made as a
simple matter  of convenience without regard  to the dangerous situation that
might  be created. And, third,  they are made with  reliance  on inadequate
protection such as a single valve or other mechanical device.
  To  combat  the dangers of cross-connections and backflow  connections,
education in their recognition  and prevention is needed. First,  plumbing
installers must know  that  hydraulic and pollutional factors may combine to
produce a sanitary hazard if a cross-connection is present. Second, they  must
realize that there are available reliable and simple standard backflow prevention
devices and methods that may be substituted for the convenient but dangerous
direct  connection. And third, it should be made clear to all that the  hazards
resulting from direct  connections greatly outweigh the convenience gained.
  This manual does  not describe all the cross-connections possible in piping

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systems. It does attempt to reduce the subject to a statement of the principles
involved and to  make it clear  to  the reader that such installations  are
potentially dangerous. The primary purpose is to define, describe, and illustrate
typical cross-connections and to suggest simple methods and devices by which
they may be eliminated without interfering with the functions of plumbing or
water supply distribution systems.

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         Chapter 2.  PUBLIC HEALTH SIGNIFICANCE OF
                       CROSS-CONNECTIONS

  According to  the official investigation of the  1933 Chicago epidemic of
amebic  dysentery, ". .. old  and generally defective  plumbing and cross-
connections potentially permitting backsiphonage from fixtures such as bath-
tubs and toilets ..." were to blame for contamination of the drinking water
supply.
  The event and its sad result — the death of 98 persons — dramatized the
concern that public health officials feel about the dangers of cross-connections.
Because  such  plumbing  defects  are so  frequent, and the  opportunity for
contaminants to invade drinking  water through cross-connections is so general,
enteric infections caused by drinking water may occur in almost any city on
any day.
  Published histories of massive enteric infections caused by cross-connections
abound.  While the following cases have their  natural appeal as historical
literature, they are listed here mainly to illustrate the serious consequences of
cross-connections, their ubiquity, their frequency, and their peculiarity.
Brucellosis at the Faucet
  In 1938, 80 students at a large mid western university reported remittent
fevers, malaise, headache, and anemia. Their symptoms led to a diagnosis of
undulant fever (brucellosis).  Curiously, only  those students who  had been
working in the cultivation of  bacteria in one of the laboratories were affected.
The mystery was how the brucella cultures  in the  laboratory  could  have been
transmitted to the students. Finally, a hose was found connected to a faucet in
the laboratory. The other  end of the hose was submerged in  water containing
brucella. A temporary reversal of pressure, possibly  the  consequence of a
demand for water in another  part of the system, had drawn the water teeming
with brucella into the drinking supply.  Of the 80 students affected, one died.
Sewage in the Water Main
  In Newton,  Kans., in 1942, one of the town's two water supply mains had
been taken out of service on September 2, 7, and 8. A house service connection
to this main supplied three frostproof hydrants and two frostproof toilets. It
was assumed,  from subsequent events, that  some unknown person or persons
tried to obtain water from a hydrant connected to the main out of service.
When no water flowed, the anonymous agents departed, leaving the valve open.
On September 10, it was discovered that a neighboring toilet sewer was clogged
and that sewage had overflowed into the hydrant box. It was learned that for 2
days all the sewage from the toilets  of 10 families had been permitted to flow
into the  water main. When the main was put back into service, there was no
attempt  to sterilize it.  More than  2,500 persons in  all  parts of  the town
suffered enteric  disorders  as a result. Stool  cultures and pathological findings

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from two autopsies diagnosed the illness as bacillary dysentery. In addition to
the widespread illness in the town, it is believed that the infection was carried
aboard a number of troop trains which were watered in Newton at that time.
Pressure Drop
  In 1942 a casting plant in Pittsburgh employing 500 persons undertook to
install new water connections.  During installation, the city water supply was
shut off. It is believed that a drop in pressure in the drinking water lines of the
plant permitted river water to pass through a valved connection to the drinking
water.  Twelve  hours  after the first new connection to the  city water was
installed, many of the employees suffered mild intestinal disorders. Two weeks
later, after  another shutdown to make a second connection  from the plant
system to the city water, there was a second outbreak of intestinal disturbances
among the employees.
Defective Valve
  Aboard a vessel in a west coast shipyard in  1943, a valve on the main line,
connecting  the drinking water to  the fire water supply, was found to be
defective  and the cause of an outbreak of gastroenteritis. The pumping of
contaminated harbor water through the fire waterlines aboard the vessel had
forced bacteria into the drinking supply  through  a cross-connection. As a
result, 1,179 men became ill.
Arsenic in Reverse
  A California laborer  had  been using an aspirator, attached to a garden hose,
to spray  a driveway with weedkiller containing arsenic. Sometime while he was
at the job, the water pressure reversed. Taking no notice of the incident,  the
man disconnected the hose and, feeling thirsty, drank from the bib of the hose
connection at the house. Arsenic in the waterline killed him.
Peak Demands
  At a  large aviation  plant on  the  west coast, officials learned  that  the
difference  between a  3-inch  water  main and an 8-inch  main  was  the
determining cause for a high rate  of absenteeism. When it was discovered that
25  to 40 percent of the  employees were suffering from gastroenteritis,  the
plumbing system was  suspected. Investigators found that there was such a
demand on the 3-inch main at peak periods that the outflow produced enough
of  a  vacuum  to  allow  waste   water  to  be  backsiphoned  through
cross-connections into  the  drinking water system. After an 8-inch main was
installed, the high rate of infection subsided.
The Vacuum Breaker
  In April 1944, after an outbreak of gastroenteritis in an Oklahoma school, it
was found that none of the flushometer  valve toilets with submerged inlets
were provided with vacuum breakers, which prevent atmospheric pressure from
forcing waste water into the supply lines. Each night, to conserve water and
eliminate the possibility that rooms might be flooded if a leak should develop,
the custodian turned off the valve of the main supply line. As the pressure in
the supply lines was cut off, atmospheric pressure on the toilet bowls moved

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the waste water up into the drinking supply. Most of the people affected were
those  who  drank from faucets on the first floor of the school; there were
progressively fewer cases on the second and third floors, as the atmospheric
pressure moved less of the waste water to those heights.
Wrong Valve
  At a school in Milford, Nebr., the fire lines and hydrants were separate from
the domestic water supply, although the two systems were connected through
a valve at the pumphouse. The source of water for the fire system was the river.
In January 1947, following a fire, someone negligently opened the connecting
valve at the pumphouse, and river water  entered the domestic water supply.
About 150 people came down with gastroenteritis.
Ten-Percent Polio Incidence
  In 1932 during a 5-week period, more than 10 percent of the  347 children in
Huskerville, near Lincoln, Nebr., contracted polio. A study of the water supply
revealed that the afflicted children lived in areas where flush valve water closets
lacked vacuum breakers. A time relationship was found also in places where
extreme fluctuations of  pressure in the  water  mains  might have permitted
waste water to be forced into the drinking supply.
Dysentery at Sea
  In 1952 a large oceangoing vessel set sail from its berth with every indication
that things were shipshape. A day or so later and  300 miles out, over a
thousand cases of dysentery developed among those on board. Contaminated
water was blamed for the episode and the evidence indicated that while tied up
at its  moorings,  the ship's fresh-water  tanks  had been  contaminated. A
cross-connection was the most likely explanation.

A Drink of Chromates
  Chromates are  one of the chemicals for which the Public  Health Service
Drinking Water  Standards  prescribe the very low amount of  0.05  parts per
million as the limit that can be tolerated in a drinking water supply. In 1958 an
employee  using a drinking water fountain in a large city library noticed that
the water stream issuing from  the spout was yellowish, and the  matter  was
called  to the attention of the building engineer. Upon investigation, it  was
found that the chilled-water pipe system supplying the fountains was directly
connected  to  another chilled-water  system in  which  heavy  dosages  of
chromates were used for corrosion control. Someone forgot to close the valve!

Harbor Water Threatens Vessel Crews
  At about 2 p.m. on June 29, 1960,  on a large  pier installation in an eastern
port harbor, a worker noticed  evidence of salt in the  potable water supply.
Investigation showed that salt  water from the harbor had been pumped into
the pier's potable water pipes. The fire  systems of three  vessels  anchored
nearby  had  been  connected  to the  fresh water  piping system  and high
fire-pump pressures apparently  did the rest. One measurement of chlorides at a

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"fresh"  water outlet  showed  6,425 parts per  million.  Only  prompt  and
vigorous action by a sanitary engineer is believed to have prevented widespread
illness.
Antifreeze
  Usually service stations supply antifreeze for automotive equipment, not for
people  to  drink. The reverse was true during October of 1961 when there
occurred one of the most bizarre backsiphonage  episodes on  record.  In  a
midwestern city, ethylene glycol  antifreeze was  being  pumped  from a  large
storage tank  to  an antifreeze distribution system. This system  was cross-
connected  to the city water supply lines and it was estimated that over 100
gallons  of  60 percent ethylene glycol  were pumped  into the  water  mains.
Samples from the water pipes showed the presence of from 1.5 to 2.0 percent
ethylene glycol, or up to 20,000 parts per million of this toxic chemical agent.
A homeowner reported a bitter taste and reddish  color to the water depart-
ment.  Radio  announcements, a shutdown of  the  water  supply to the  area
affected, and repeated flushings were required to cope with the situation.
Outbreak Fells Shipyard Workers
  The  time was 7 a.m. on  September 28, 1962, at a  large eastern shipyard.
Beginning  then  and throughout the  day, some  700 men reported ill  with
gastroenteritis. All had drunk water from the yard area where they worked and
one  water sample  showed coliforms in  excess  of 240 per  100 milliliters.
Investigators concluded  that a temporary cross-connection  had been made
between the potable  water lines  and  pipes containing  river  water  for
firefighting purposes. They stated that ". . .  such an episode  may occur again
if steps  are  not taken to  insure  that  such  ill-considered cross-connections
cannot be made by accident."

  The following incidents occurred after the publication of the first edition of
this manual. They show that cross-connection continues to be a serious hazard
to water supplies and only constant vigilance in their detection and elimination
can reduce the ever-present risk of contamination from these sources.

Arsenic Poisoning
  On a private farm  in Texas in 1963, five people were  poisoned with arsenic
from drinking water. The  source  of  drinking  water was a cistern.  A cotton
defoliant tank which  contained  arsenic  was  improperly connected to  the
cistern. Backsiphonage occurred, and of the five people  who drank the water,
three died.
Nurses 111
  Backsiphonage caused by defective  plumbing in a new  student  nurses

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building was  blamed for an  outbreak of disease in 1963 in Ohio. It  was
necessary for 100 of the  student  nurses to  be quarantined for  2 weeks.
Bacteriological examination  showed that the drinking water was contaminated.
The city health  commissioner theorized that salmonella was brought into the
building by some of the girls and then spread by defective plumbing.

Eleven Vomiting Caddies
  Eleven caddies experienced  nausea, severe vomiting, and abdominal cramps
after consuming a "soft drink" at a New York golf club in 1964. The beverage
was commercially prepared by the mixture of sirup with carbonated water in a
vending machine.  Investigation revealed that a pipe carrying  water  into the
machine was connected to the recirculating hot water heating system instead of
the drinking  water system.  The day before the incident a lye and chromate
solution was added to the hot water system.

Raw Water From a Drinking Fountain
  A New England town had two separate water systems — one for potable
water,  the other  for fire protection.  The fire  protection system  pumped
untreated water  directly from  a river. In 1967,  at an industrial plant in town,
workers mistook a fire system line for a fresh-water  line  and connected a
bubbler  to it. After drinking the water from  the bubbler, seven people
developed infectious hepatitis and over  a  hundred people  were  ill with
gastroenteritis.

Shigellosis
  In 1967, an outbreak of gastroenteritis occurred at a small private college in
Pennsylvania. Almost  one-quarter  of  the 700  students  and faculty were
affected.  The only  factor in  common to all those  who became ill was the
consumption of water or food that had been prepared using  water from the
school water system. Investigation of the  water system  revealed that a water-
line had broken in the kitchen of the school cafeteria flooding both the kitchen
and the cafeteria. Cross-connections were found between the sewage system
and the fresh-water system that could have resulted in backsiphonage of sewage
into the water system as a consequence of negative pressure during the break in
the waterline. It was concluded that the outbreak probably resulted from the
presence of Shigella sonnet in the water system. The inoculum would have been
of sufficient size to overcome the chlorine in the water.

Football Team Stricken
  In October 1969, most of the members and  coaches of a  college  varsity
football team became ill  with infectious  hepatitis. The  water supply on the
practice field was found to be the cause. A drinking fountain and the irrigation
system for the field were on the same line. A heavy fire demand in the area had
created a negative pressure in  the waterlines and  caused contaminated surface
water around the sprinklers to be siphoned into  the potable water lines. Players
and coaches  drinking from the fountain became ill and the school was forced
to cancel the remainder of the football schedule.

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Temporary Hydrant Connections
  A serious emergency involving  the  contamination of a water supply was
caused by a truck filling from a city water supply. In 1971, a contractor using a
tank truck with a rig designed to pump and spray a mixture of water, fertilizer,
grass seed, and woodpulp was working on the grounds of a-sub division. The
contractor was using a direct connection to a fire hydrant to fill the tank with
water,  which was then mixed with the fertilizer,  etc. A high-pressure pump
then sprayed  the mixture  onto  the  ground. As the woodpulp  circulated
through the tank piping system, it plugged one of the lines while the pump
continued to run creating a very high  pressure in the tank. This pressure was
higher  than  the water supply system  pressure and it forced the solution  of
fertilizer into  the water system. Several people in the subdivision became ill
after drinking  the water, but the contamination was discovered and quick
action in flushing and disinfecting the lines eliminated the danger.

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            Chapter 3.  THEORY OF BACKFLOW AND
                          BACKSIPHONAGE

  A cross-connection1  is the link or channel connecting a source  of pollution
with a potable water supply. The polluting substance, in most cases a liquid,
tends to enter the potable supply if the net force acting upon the liquid acts in
the direction  of the potable  supply. Two factors are therefore  essential for
backflow. First, there  must be  a link between  the two systems. Second, the
resultant for ce must be toward the potable supply.
  An understanding of the principles of backflow and backsiphonage  requires
an understanding of the terms frequently used in their discussion. Force, unless
completely resisted,  will produce  motion. Weight is a type of force resulting
from  the  earth's gravitational attraction. Pressure (P) is a force-per-unit  area,
such  as pounds per square inch (psi). Atmospheric pressure is  the pressure
exerted by the weight of the atmosphere above the earth.
  Pressure may be referred to using an absolute scale, pounds per square inch
absolute (psia),  or gage scale, pounds per square inch gage (psig). Absolute
pressure and gage  pressure are related. Absolute pressure is equal to the gage
pressure plus the atmospheric pressure. At sea level the atmospheric pressure is
14.7 psia. Thus,


                       P  absolute  = P gage +14-7 Psi
or
                      P  gage      =  P absolute ~14-7 Psi
  In essence, then,  absolute  pressure is the total pressure. Gage pressure  is
simply the pressure  read  on a gage. If there is no pressure on the gage other
than atmospheric, the gage would read zero. Then the absolute pressure would
be equal to 14.7 psi which is the atmospheric pressure.
  The term vacuum  indicates  that the absolute pressure is  less than the atmo-
spheric  pressure and that the gage pressure is  negative. A complete or total
vacuum would mean a pressure of 0 psia or -14.7 psig. Since it is impossible to
produce a total vacuum,  the  term vacuum, as  used in the text, will mean all
degrees of partial vacuum. In  a partial vacuum, the pressure would range from
slightly less than 14.7 psia (0  psig) to slightly greater than 0 psia (-14.7 psig).
  Backsiphonage1 results in fluid flow in an undesirable or  reverse direction. It
is caused  by atmospheric pressure exerted on a pollutant liquid forcing it
toward a  potable water supply  system that  is  under a  vacuum. Backflow,

  1 See formal definition in the glossary of the appendix.

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although  literally meaning any  type  of reversed  flow, refers to  the  flow
produced by the differential  pressure existing between two  systems both of
which are at pressures greater than atmospheric.
Water Pressure
  For an  understanding of the nature of  pressure and its relationship to water
depth, consider the pressure exerted on the base of a cubic foot of water at sea
level. (See tig.  1.) The average weight of  a cubic foot of water is 62.4 pounds.
The pressure exerted upon the square foot area is, therefore, 62.4 pounds per
square foot gage. The base may be subdivided into 144 square inches with each
subdivision being subjected to a pressure of 0.433 psig.
         FlGURK  1.  Pressure exerted b> I fool of water at sea level.

  Suppose another cubic  fool of water were placed directly on topol the first,
(Sec fig.  2.) The  pressure  on  the  top surface of (lie first cube which was
originally atmospheric, or 0 psig. would now  be 0.433 psig as a result of the
superimposed cubic foot of water.  The pressure at the base of the first cube
would also be  increased b\ the same amount  to 0.866 |»ig. or two limes the
original pressure.
  II  this process were repeated  with a third cubic foot of water, the pressures
at the  base  of each  cube would be 1.299 psig, 0.866 psig, and  0.133 psig,
respectively. It is  evident that  pressure varies  wilh depth bclou  a free water
surface.  In general, each loot of elevation change, within a liquid, changes the
pressure by an amount equal to  the weight-per-unit area of I  fool of the liquid.
The  rate of increase for water is  0.133 psi per foot of depth.
  Frequently water pressure is referred to  using the terms  'pressure head  or
just  "head," and is expressed in units of feet of water. ( hie loot of  head would
be equivalent to the pressure produced at the base of a column of water 1 foot
in depth. One  foot of head or 1 foot of water is equal  to 0.433 psig. One
hundred leet ol head are equal to 43.3 psig.
   Sec formal definition in the glossary of the appendix.
10

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                                                       0.433  PSIG
                                                      0.866 PSIG
         FIGURE 2.  Pressure exerted by 2 feet of water at sea level.


Siphon Theory

  Figure 3 depicts the atmospheric pressure on a water surface at sea level. An
open tube is inserted vertically into the  water; atmospheric pressure, which is
14.7 psia, acts equally on the surface of the water within the tube and on the
outside of the tube.
                        14.7
                        PSIA
14.7
PSIA
14.7
PSIA
                                                    Sea  Level
       FIGURE 3.  Pressure on the free surface of a liquid at sea level.
                                                                  11

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  If, as shown in figure 4, the tube is tightly  capped and a vacuum pump is
used to evacuate all the air from the sealed tube, a vacuum with a pressure ol 0
psia is created within the tube. Because the pressure at any point in ;i static
fluid is dependent upon  the height of that point above a reference line, such a>
sea  level, it  follows that  the pressure within the tube at sea level must  still be
14.7 psia. This is equivalent to  the pressure at  the base of a column  ol  v\aler
33.9 feet high and  with  the column open at the base, water would rise to lill
the  column  to a  depth of  33.9 feet. In  other words,  the  weight  ol  the
atmosphere  at sea level exactly  balances the weight of a column of water 33.9
feet in height. The absolute pressure within the column of water in figure 4 at a
height  of 11.5  feet  is equal  to 9.7 psia.  Ill's is  a partial vacuum with an
equivalent gage pressure of -5.0  psig.



i




;




33.9'





14.7
PSIA
\





r

(Cy"Zero" Absolute Pressure
IT
:
0.0
PSIA















! j




1
9.7
»SIA
.
4.7
»SIA
f

":"%,
:::::;^=Q3g)
or -14.7 Vacuum
Pump







or-5-0
PSIG
~f~
"j5 14.7 0.0
PSIA ° PSIG
w y Sea Level

             FIGURE 4.  Effect of evacuating air from a column.
 12

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  As a practical example, assume the water pressure at a closed faucet on the
top of a  100-foot-high building to be 20 psig; the pressure on the ground floor
would then be  63.3 psig.  If the pressure at the ground were to drop suddenly
due to a heavy fire  demand in  the area to 33.3 psig, the pressure at the top
would be reduced to -10 psig. If the building water system were airtight, the
water would  remain at the level of the faucet because  of the partial vacuum
created by the  drop in pressure.  If the  faucet were  opened, however, the
vacuum would  be broken and the water level  would drop to a height of 77 feet
above the ground. Thus, the atmosphere was supporting a column of water 23
feet high.
  Kigure 5 is a diagram of an inverted U-tube that has  been  filled with water
and placed in two open containers at sea level.
                                         4.7 PSIA
    10.3 PSIA
10.3 PSIA
     FIGURE 5.  Pressure relationships in a continuous fluid system at the
                 same elevation.

  If the open containers are placed so that  the liquid levels in each container
are at the same height, a static state will exist; and the pressure at any specified
level in either leg of the U-tube will be the same.
  The  equilibrium condition is altered by raising one of the containers so that
the liquid level in one container is 5 feet above the level of the other. (See fig.
6.) Since both containers  are open to  the  atmosphere,  the  pressure on the
liquid surfaces  in each container will still  remain at 14.7  psia.
  If it  is assumed that a static state exists, momentarily, within the system
shown  in figure  6, the pressure in the left tube at any height above the free
surface in the left container can be calculated. The pressure at the correspond-
ing level in  the right tube above the free surface in the right container may also
be calculated.
                                                                       13

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  As shown in figure 6, the pressure at all levels in the left tube would be less
than at corresponding levels in the right tube. In  this case, a static condition
cannot  exist because fluid will flow  from the higher pressure to the lower
pressure; the flow would be from the right tank to the left tank. This arrange-
ment  will be recognized as a siphon.  The crest of a siphon  cannot be higher
than  33.9 feet  above the upper  liquid level, since the atmosphere cannot
support a column of water greater in height than 33.9 feet.
8.2 PSIA
'


1
14.7
PSIA



i^ 	 __^_

f


5'


'


j







-^






5'
-/I
' 1

y


\
\


\



\





V-



\
. ,




-^




10.3 PSIA
4 14.7
10- PSIA
I1^
x ^\
\
J
•
	 J)



       FIGURE 6.  Pressure relationships in a continuous fluid system at
                   different elevations.

  Figure 7 illustrates how this siphon principle can be hazardous in a plumbing
system.  If the supply valve  is closed, the  pressure in  the  line supplying the
faucet is less than the pressure in the supply line to  the bathtub. Flow will
occur, therefore, through siphonage, from the bathtub to the open faucet.
  The siphon actions cited have been produced by reduced pressures resulting
from  a  difference  in the  water  levels at two  separated points  within  a
continuous fluid system.
  Reduced pressure may also be  created within  a fluid system as a result of
fluid motion. One of the basic principles of fluid mechanics is the principle of
conservation of  energy. Based upon this principle, it may be shown that as a
fluid accelerates, as shown in figure 8, the  pressure is reduced. As water flows
through a  constriction such  as a converging section of pipe, the velocity of the
water increases; as  a  result, the pressure is reduced. Under such conditions,
negative pressures may be developed in  a pipe. The simple aspirator is based
upon  this  principle. If this point of reduced pressure is linked to a source of
pollution, backsiphonage of the pollutant can occur.

14

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                         Valve Open
    Submerged Inlet   r—  I
              FIGURE 7.  Backsiphonage in a plumbing system.
        FIGURE 8.  Negative pressures created by constricted flow.

  One  of  the  common  occurrences of dynamically reduced pipe pressures is
found  on  the suction  side  of  a  pump.  In many cases similar to the one
illustrated in figure 9, the line supplying the booster pump is undersized or
does not have  sufficient pressure to deliver water at the rate at which the pump
normally operates. The  rate of flow in the pipe may be increased by a further
reduction  in pressure at the pump intake. This often results in the creation of
negative pressure. This negative pressure may become low enough in some cases
to cause vaporization  of the water in the line.  Actually, in  the illustration
shown, flow from the source of pollution would occur when pressure on the
suction side of the pump is less than pressure of the pollution source; but this
is backflow, which will be discussed below.
  The  preceding discussion has described some of the means by which negative
pressures  may be  created  and which frequently occur to  produce  back-
siphonage. In  addition to the negative pressure or reversed force necessary to
cause backsiphonage and backflow, there must also be the cross-connection or

                                                                      15

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                                                        To
                                                        Fixture
                                 Booster Pump
              FIGURE 9.   Dynamically reduced pipe pressures.

connecting link between the potable water supply and the source of pollution.
Two basic types  of connections  may be created in piping systems. These are
the solid pipe with valved connection and the submerged inlet. Figures 10 and
11 illustrate solid connections. This type of connection is often installed where
it is necessary to  supply an auxiliary piping system from the potable source. It
is a direct connection of one pipe  to another pipe or receptacle.
  Solid pipe  connections are often made to continuous or intermittent waste
lines where it  is assumed  that the flow will be in one direction only. An
example of this would be used cooling water from a water jacket or condenser
as shown  in  figure 11. This type of  connection  is  usually detectable  but
creating a concern on the part of the installer about the possibility of reversed
flow is often more difficult. Upon questioning, however, many installers will
agree that the solid connection was made because the sewer is occasionally
subjected to backpressure.
  Submerged inlets  are found  on many common plumbing fixtures and are
sometimes necessary features of the fixtures  if they are to function properly.
Examples of this  type of design are siphon-jet urinals or water closets, flushing
rim slop sinks, and dental cuspidors. Oldstyle bathtubs and lavatories had
supply  inlets  below the  flood level rims, but modern sanitary  design  has
minimized or  eliminated this hazard in new fixtures. Chemical and industrial
process vats sometimes  have submerged inlets  where the water pressure is used
as  an  aid in diffusion, dispersion, and agitation  of the  vat contents. Kven
though the supply pipe  may come from the floor above the vat, backsiphonage
can occur as it has been shown that the siphon action can raise a liquid such as
water  almost  34 feet.  Some submerged inlets difficult to  control are those
which  are not apparent  until a significant change in water level occurs or where
a supply may be conveniently extended below the liquid surface by means of a
hose or auxiliary  piping. A submerged inlet may be created in numerous ways,
and its detection in some of these subtle forms may be difficult.

16

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        Nonpotable                                      Potable

FIGURE 10.  Valved connection between potable water and nonpotablc fluid.

                                    Condenser
                              f(
     Sanitary Sewer
  FIGURE ll.   Valved connection between potable water and sanitary sewer.

  The illustrations included in part B of the appendix are intended to describe
typical examples of baeksiphonage, showing in each case the nature of the link
or cross-connection, and the cause of  the negative pressure.
Backflow
  Backflow,  as described in this manual, refers to reversed flow due  to back-
pressure other than siphonic action. Any interconnected fluid systems in which
the pressure of one exceeds the pressure of the other may have flow from one
   See formal definition in the glossary of the appendix.

                                                                      17

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to the other as a result of the pressure differential. The flow will occur from
the  zone of  higher  pressure to the  zone of lower pressure.  This  type of
backflow is of concern in buildings where two or  more piping systems are
maintained. The potable water supply is usually under  pressure directly from
the  city water main. Occasionally, a booster pump is used. The auxiliary
system is often pressurized by a centrifugal pump, although backpressure may
be caused by gas or  steam pressure from a boiler. A reversal in differential
pressure  may  occur when pressure in the potable  system  drops, for some
reason, to a pressure lower than that in the system to which the potable water
is connected.
  The most positive method of  avoiding this type of backflow is the total or
complete separation  of the two systems. Other methods used involve  the
installation of mechanical devices. All methods require routine inspection  and
maintenance.
  Dual piping systems are often installed for extra protection in the event of an
emergency or possible mechanical failure of one of the systems. Fire protection
systems are an example. Another example is the use of dual water connections
to boilers. These installations are sometimes interconnected, thus  creating a
health hazard.
  The illustrations in part C of the  appendix depict  installations where back-
flow under pressure can occur, describing the cross-connection and the cause of
the reversed flow.
18

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         Chapter 4.   METHODS AND DEVICES FOR THE
               PREVENTION OF BACKFLOW AND
                        BACKSIPHONAGE

  The control  of backflow  and backsiphonage requires either the complete
removal of the cross-connection or the installation of a proper cross-connection
control device. Removal of the physical link is preferred because it eliminates
the possibility  of  failure of  a mechanical device.  However, the operation of
some fixtures, such as a siphon-jet water closet, requires a link in the form of a
submerged outlet. In this case,  an acceptable cross-connection control device
should be employed to  reduce the hazard significantly. There are no cases
where a cross-connection cannot be removed or corrected.
Airgap Separation
  The only absolute  means of eliminating the physical link is  through the use
of the vertical airgap, as illustrated  by figure 12. Airgaps should  be used
wherever possible, and where  used must not be bypassed.
                                            Flood Level Rim
                    FIGURE 12.  Airgap on lavatory.
                                                                  19

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  The  supply  inlet to the  fixture should be terminated above the flood-level
rim of the  fixture by  a distance  equal  to  at  least two times the effective
opening1 of the fixture. Ideally, there should  be no provision for extending the
fixture outlet below  the flood-level rim. If the  end of the  supply  pipe  is
threaded or serrated to permit the  connection of a hose, however, a properly
installed vacuum breaker should also be provided.
  Some examples of generally used plumbing fixtures are shown in table 3.82
in chapter 7, subsection 3.82, page 39.
  If an airgap  separation is provided at each  fixture, complete  protection will
be  provided  within  the building  as well as to the municipal supply. The
separation may also be made at one point where the water service enters the
building.  It  must  be  remembered, however,  that this  protects only the
municipal water supply system and not the building system.
Surge Tanks
  A surge tank, illustrated in figure 13, consists of a reservoir and  pump
combination with the potable water supply to the reservoir delivered through
an airgap. The size of each unit is determined by the water demand rate which
it is to accommodate.  The rate of flow into the receiving reservoir of the simple
surge tank shown in figure 13 is governed by the  float valve. The booster pump
draws  water from  the reservoir, or surge tank, and  discharges  directly to the
distribution  system under pressure.  When the discharge of the booster pump is
to serve points where water will be withdrawn for domestic use, the surge tanks
should be covered  properly to prevent contamination. The surge tank is often
used in installations where  water  is  needed in industrial processes and may be
used to serve single fixtures, equipment units, or entire systems.
       Butterfly
         Valve
To Chemical Process
or other Nonpotable
       Use Fixture
 \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
                FIGURE 13.   Surge tank and booster pump.
  'See glossary in appendix.

20

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Color Coding
  When  two  or  more piping  systems are used for water in a building or
industrial plant, extreme care should be taken not to interconnect the systems.
There may be a potable water system and systems carrying lesser quality water
such as for fire protection. To  help prevent the possibility of the two systems
being interconnected, pipes  should be identified  adequately  by legends  and
color coding based on the American Standards Association Scheme for Identifi-
cation of Piping Systems (ASA A13.1-1956).
  Color coding should not be used solely to identify the contents of pipes but
should b6 used supplementary to the use of legends. Potable water lines should
be  painted  green or  with bands of  green and the words "potable  water"
stenciled  on the pipe  at appropriate intervals. Pipes  carrying water for  fire
protection should be painted  red and be stenciled. Piping systems carrying
other material or water for  other purposes should  also be clearly identified
with the  appropriate legends and color  coding.
Booster Systems
  Booster pumps are often required in high buildings. Frequently these booster
pumps are connected directly  to  the city water main  or water service, under
which conditions there is always the possibility of creating a negative pressure
in the water main, as shown in figure 22 of appendix  B. A simple surge tank
could be used to protect the city main in such cases. Its disadvantage is that all
or most  of the city water pressure which otherwise  might be available  is  lost
through  the  airgap. Also there is the hazard of introducing contamination
through  the surge tank. A pressure limiting switch  can be connected to the
booster pump suction to prevent the pump from creating negative pressures in
the main, but  operators find it convenient to shunt around such a switch if
there is any interruption in service. Figure 14 illustrates a positive method of
negative  pressure control, which at the same time permits the direct use of  city
pressure  when the pressure is  adequate.
  When the  city pressure is sufficient,  the booster pump is operated with  full
city pressure applied to the intake side of the pump. An altitude, or pressure-
reducing  valve, is  installed  below the  reservoir  to  minimize the required
reservoir height.  If the pressure in the water main  drops below the pressure
differential of the pressure-reducing valve, air is drawn in through the pressure-
reducing valve, airbinding the pump and causing it to stop. If airbinding the
pump is  undesirable, a low-water-level pump shutoff switch may be added to
the unit.
Vacuum  Breakers
  A fundamental factor in backsiphonage, as outlined  in chapter 3, is vacuum
or negative pressure.  If atmospheric pressure is admitted to a piping system
between  a source of pollution and the origin of the vacuum, backsiphonage will
be prevented. This is the function of a vacuum breaker. It  is not designed to
provide protection against backflow resulting from  backpressure, and should
not be installed  where backpressure may occur. Because a vacuum may be
created  at numerous  places  in a piping  system, a  vacuum breaker must be

                                                                       21

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                        Screened Vent
                                      .——
                                      Water Level
                      FIGURE14.  Booster system.

located as  near  as possible  to  the fixture  from  which  contamination  is
anticipated. The position of a vacuum breaker must be sufficiently above the
fixture flood-level rim so that flooding or submergence of the vacuum breaker
or backpressure cannot occur.
  A vacuum breaker may be  installed either on the atmospheric side of a valve
or within  a pressurized distribution system.  A non-pressure-type  vacuum
breaker is installed on the atmospheric side arid will operate or cycle each lime
the valve is used.  This type should not be installed where it will remain under
pressure  for long periods.  A pressure-type vacuum breaker is  installed in a
pressurized system and will operate only when a  vacuum occurs The device is
usually  spring loaded, and  il should be specially designed to  operale after
extended periods under pressure because corrosion and deposition of material
in the line might render it inoperable.

22

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  Installation of a vacuum breaker on the atmospheric side of the last control
valve is always preferred and recommended because, by virtue of its position, it
prevents  any contamination from  being siphoned into the water system. A
vacuum  breaker installed somewhere  in the  pressurized system  does not
completely protect the system, and could,  with certain piping arrangements,
allow backsiphonage into the water system. Vacuum breakers should be used in
a pressurized  system only on specific authorization of the  administrative
authority having jurisdiction.
  The operation of one type of vacuum breaker is illustrated in figure 15. The
flow of water  is downward and the disc  is seated in the vertical  position,
preventing  water from spilling out the  pipe (view 1). If a negative pressure
should develop in the supply line, atmospheric  pressure would force the disc
into the  horizontal  position, thereby  blocking the supply line, admitting air,
and preventing backsiphonage (views 2 and 3).

                                                Vacuum
  Disc
                           Atmospheric/
                              Pressure
                            N. Atmospheric
                                 Pressure
       Disc in  Normal
        Flow  Position
Vacuum
          Atmospheric
             Pressure
  Flow  Just after
Vacuum is  Applied
            ^Atmospheric
               Pressure
                       Disc  in  Vacuum
                      Breaking Position

               FIGURE 15.  Operation of a vacuum breaker.
                                                                     23

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  Figure  16  shows a  non-pressure-type vacuum  breaker  installation.  The
 serrated outlet laboratory sink supply might easily be extended by a hose to a
 point below the flood-level rim of the laboratory sink, thus producing a cross-
 connection. The vacuum breaker installation on  the atmospheric  side of the
 control valve and between the cross-connection effectively protects the piping
 system against backsiphonage.

                                                        Vacuum
                                                        Breaker
    FIGURE 16.  Typical non-pressure-type vacuum breaker installation.

Reduced Pressure Zone Backflow Preventer
  In situations where  it would be extremely  difficult to provide a physical
break between two systems and where  backpressures  can be expected, a
reduced  pressure  zone backflow  preventer (RPZ) can be used.  This device
consists of two,hydraulically or mechanically loaded, pressure-reducing check
valves, with a pressure-regulated relief valve located between the two  check
valves as shown by figure 17.
  Flow from the left enters the central chamber against the pressure exerted by
the loaded check valve 1. The  supply pressure is reduced thereupon by a
predetermined amount. The pressure in the central  chamber  is  maintained
lower then the incoming supply pressure through  the operation of the relief
valve  3,  which discharges to the atmosphere  whenever the central chamber
pressure approaches within a few pounds of the inlet pressure. Check valve 2 is
lightly loaded to open with a pressure drop of 1  psi in the direction of flow and
is independent of the pressure required to open the relief valve. In the event

24

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    Normal Direction of Flow
Reversed Direction of Flow
        FIGURE 17.  Reduced pressure zone backflow preventer
                         principle of operation.
that the pressure increases downstream from the device, tending to reverse the
direction of flow, check valve 2 closes, preventing backflow. Because all valves
may leak  as a result  of wear or obstruction,  the protection provided by the
check valves is not considered  sufficient. If some obstruction prevents check
valve 2 from closing tightly, the leakage back into the central chamber would
increase the pressure in this zone, the relief valve would open, and flow would
be discharged to the atmosphere.
  When the supply  pressure drops to the minimum differential required  to
operate the  relief valve, the  pressure  in the central chamber  should  be
atmospheric.  If  the  inlet  pressure  should  become less than atmospheric
pressure, relief valve 3 should remain fully open to the atmosphere to discharge
any  water which may be caused to backflow as a result of backpressure and
leakage of check valve 2.
  Malfunctioning of one  or both of the check valves  or relief valve should
always be indicated by a discharge of water from  the  relief port. Under  no
circumstances should plugging  of the relief port be permitted because the
device depends upon an open port for  safe operation. The pressure loss through
the  device may  be  expected to average between  10 and 20 psi  within the
normal range  of operation,  depending upon  the  size  and flow rate of the
device.

Double Check Valve Assembly and Other Methods
  Other  methods and  devices  have  been promoted for the separation  ot
auxiliary systems or for the prevention of backflow.  Among these are the single
check  valve, and plain double  check valve assembly, the double check valve-
double gate valve assembly, the  swivel connection, and the  barometric loop.
  The single check valve  offers no visual or mechanical means of determining
malfunctioning,  and  since  all  mechanical devices  are subject to wear and
interference resulting from deposits and other factors, the single check valve is
not considered an adequate backflow preventer. Double check valve assemblies

                                                                       25

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 in series, including those with spacers  and manual bleed valves, have similar
 disadvantages.  The advantage offered by the manual bleed valve is usually
 negated by the human element which may cause the valve to remain closed.
  The  double check-double  gate valve assembly, shown  in  figure 25 of
 appendix B, is a very useful and, when properly maintained, reliable means of
 backflow protection for intermediate degrees of hazard. This device has been in
 service at some plants since the early 1900's. As in the case of other backflow
 preventers, the double check-double gate valve assembly should be inspected at
 regular intervals. Some health authorities have established programs of annual
 inspection.
  The double check-double gate system has the advantage of a low head loss.
 With the gate valves wide open the two checks, when in open position, offer
 little resistance to flow.
  Double check-double  gate  assemblies  should  be well designed and con-
 structed. The valves should be all  bronze or, for larger sizes, galvanized gray
 iron. The  trim should  be of bronze,  or other  corrosion-resistant  material.
 Springs  should be bronze, stainless  steel, or spring steel covered with a coat of
 vinyl plastic. Valve discs should be of  composition material with low water
 absorption properties. Test cocks should be provided.
  The swivel connection does not offer adequate protection against backflow
 between the two  systems that it  interconnects.  It should not be  used to
 connect  a hazardous system  to a potable system without the inclusion of an
 acceptable means of backflow prevention.
  The barometric loop consists of a vertical loop of pipe extending at least 35
 feet  above the highest fixture. The  principle is that a complete vacuum cannot
 raise water to an elevation greater than 33.9 feet. The device, however, does
 not  provide protection  against  backflow  due  to  backpressure  and  the
 installation of a pipe loop of this height is usually difficult and expensive. As a
result it is not widely used.
26

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      Chapter 5.  TESTING PROCEDURES FOR BACKFLOW
                            PREVENTERS

Vacuum Breakers
  A vacuum breaker  should be  subjected to  routine visual  inspection to
determine  that the  device  is  functioning normally. Malfunction  may be
indicated by excessive weeping or  leakage of the device. Stains or watermarks
on the outside body of the device may also indicate malfunction.
  Internal inspection should also be made periodically. Rubber membranes and
gaskets, valve seats, and the internal mechanism should be carefully inspected
for rupture, scoring of metal, scaling, corrosion, or any accumulation of dirt or
foreign matter that would prevent the safe operation of the device.
  A complete  inspection of a  vacuum breaker installation also includes a
determination that the device has not been bypassed and that under no con-
ditions could  it be  subjected  to  backpressure. Vacuum  breakers must be
installed above the flood-level rim of  the equipment supplied and should be
located at  the  highest point in  the  part of the  water system served so as to
preclude any  possibility of  backpressure  being applied  to the device. A
complete  record,  including  date  of  installation  and information  on  all
inspections,  tests,  and repairs,  should be maintained on  each device. Any
defects found  during inspection or testing  should be  corrected immediately
before allowing the device to be placed back in service.
  The basic concept in testing of  a  vacuum breaker for proper operation
involves a determination that the air inlet will open fully when there is little or
no  water  pressure inside the device.  The canopy  or  hood on the  vacuum
breaker should  be removed,  where possible,  to expose the air inlet. When
testing a non-pressure-type vacuum breaker, the closest upstream valve should
be  opened  to  allow  water to fill  the  downstream  piping.  The valve  is then
closed; the vent ports should open allowing air to enter the device and water to
flow out the downstream piping. If water does not continue  to flow, or if there
is a mere  trickle, the vacuum breaker is not opening properly. The defect
should be corrected immediately  and the device retested.
  When testing a  pressure-type  vacuum breaker, the  system  must first be
under  pressure. (See fig. 18.) First  valve 2 is closed, then valve 1. The test cock
should then be opened to lower the pressure and allow water to drain slowly
from the device. As the pressure in the device  drops to near 0 psi, the air inlet
should open automatically if it  is operating properly. If the air inlet remains
closed, the valve or spring may be corroded or fouled causing it to cement shut.
The defect should be corrected  immediately by  installing a new  vacuum
breaker or  by repairing the old one and retesting. Next, the system should be
repressurized by closing the test  cock and opening valve 2 and then valve 1. As
the pressure increases, some water  should discharge through the vent ports. If
the discharge continues as the system is repressurized, however,  it means that

                                                                      27

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             Valve  2
                                                          Test  Cock
                                                        Valve 1
           FIGURE 18.  Pressure-type vacuum breaker installation.

the valve has not seated properly and may be damaged or fouled. The defect
should be corrected immediately and the device completely retested.
Reduced Pressure Zone Backflow Preventer
  In the operation of an RPZ, the reduced pressure zone between the two
check valves is maintained at a pressure less than the supply  pressure by the
action  of  the  pressure differential relief  valve. The  relief valve should  be
capable of  maintaining a reduced pressure zone, which is at least 2 psi less than
the supply pressure. If the supply pressure becomes less than  2 psi, the relief
valve  opens  and  the  pressure in  the  reduced  pressure  zone  becomes
atmospheric. When field testing an RPZ, it should be observed that the device
has not been bypassed and that the relief valve can freely discharge water. The
device should  undergo periodic internal  inspection and should be cleaned or
repaired as necessary. Check  valves and the pressure differential relief valve
should be  checked for wear, corrosion, scaling, fouling, or other  damage that
may cause malfunction.
  Occasional  discharge  of  water through  the relief valve can be caused  by
fluctuations in  inlet pressure, and usually occurs when there is no flow through
the device. Continuous  discharge  of  water through  the relief  valve under
flowing conditions indicates either  that  the relief valve  is malfunctioning or
that check valve 1 is held in an open  position. (See fig.  17.) Continuous
28

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discharge under no-flow conditions indicates that the differential relief valve is
malfunctioning, or that there is a leak in check valve l,or that a backflow
condition exists and check valve 2 is leaking.
Test Procedure
  A field test of the device is used to determine if the pressure relief valve and
the two  check valves are operating properly. A differential pressure gage with a
0-15-psi  range and a working pressure  of 500 psi and appropriate lengths of
hose with necessary fittings are needed for testing. (See fig. 19.)
           Cheek Valve No. 1—)   /Differential
                                /   Pressure
Gate Valve No. 1,           |  \ Re|ief  Valve
                               A
             Valve "A"

              Valve "B
    Check Valve No.  2

       Gate Valve No.  2
                                                       Test  Cock  No. 4

                                                    Test Cock  No. 3
     Bypass  Hose
Air Vents
Differential
Pressure Gage


  Valve "C"
                                        x Bypass Valve

      FIGURE 19.   Reduced pressure zone backflow preventer field test.
  Step  Number 1.  Steps  for testing  check valve 1  for  tightness against
backflow and measuring the pressure differential:
    A. Open all test cocks individually to flush out any dirt and sediment and
       then close.
    B. Close gate valve 2 and open gate valve 1. If there is no  drainage from the
       relief valve, check valve 1 is closed tight.
    C. Connect test hose between test cock 2 and valve B, and between test
       cock  3 and valve C.
    D. Close valve A and gage bypass valve.
    E. Open test cocks 2 and 3.
    F. Open valves B  and C. Open air vents on gage to clear all air, then reclose.
                                                                       29

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    G. Open test cock 4 and allow it to drain slightly until gage reading stops
       rising, then reclose and read differential gage pressure, which should be
       above 5 psi.

  Step Number 2.  Steps for determining the differential pressure at which the
pressure differential relief valve will open:
    A. With pressure holding constant above 5 psi, open very slowly the gage
       bypass  valve until pressure starts to drop slowly.
    B. When the  first drops of water discharge from the pressure relief valve,
       pressure reading should not be below 2 psi.
    C. Close bypass valve.X0pen test cock 4 and allow it to drain slightly until
       gage reading stops rising. Then close test cock 4.

  Step Number  3.  Steps for  testing check  valve 2  for tightness against
backflow:
    A. With pressure holding constant above 5 psi, connect hose from valve A
       to test  cock 4. Slowly open valve A and vent air from hose connection
       at test cock 4. Tighten connection and open test cock 4.
    B. Differential pressure reading should not drop below 5 psi.

Double Check-Double Gate Valves
  The  double  check-double gate valve assembly should  include test cocks as
shown in figure 20. A method for testing the check valves is as follows:
                 Gate A
Gate  G
    Public
    Supply
Test Cocks
         Private
         Supply
               FIGURE 20.  Method of testing check valves.

  A. Where Backpressure Is Available on Private Supply.

    1. Open all test cocks individually to flush out any sediment or scale.
    2. Close gate valves A and G.
    3. Open test cocks B and F, successively. If leakage occurs, gate valve(s) A
      and/or G are leaking and must be repaired before continuing test.
    4. a. Open gate valve G and test cock D. If leakage does not cease, check
        valve E is leaking  and  must be repaired. If leakage ceases, check valve
        E is tight.
      b. Temporarily connect  a hose  between test  cocks D and F and open
30

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       both. Open test cock B. If leakage does not cease, check valve C is
       leaking and must be repaired. If leakage ceases, check valve C is tight.
    c. If check valves are repaired, repeat the test as above.
  5. When the test is complete, close test cocks and remove the hose. Leave
    gate valves A and G in their proper position.

B. Where Insufficient Backpressure Is Available on Private Supply.

  1. Open all test cocks individually to flush out any sediment or scale.
  2. Close gate valves A and G.
  3. Open test cocks B and F, successively. If leakage occurs, gate valve(s) A
    and/or G are leaking and must be repaired before continuing test.
  4. a. Temporarily  connect  a hose between test  cocks J  and F and  open
       both. Open test cock D.  If leakage does not cease, check valve E is
       leaking and must be repaired. If leakage ceases, check valve E is tight.
    6. Close cocks  J  and F. Temporarily connect the hose between test
       cocks J and D and open both. Open test cock B. If leakage does not
       cease, check valve C  is leaking and must be repaired. If no leakage
       occurs, check valve C is tight.
    c. If check valves are repaired, repeat the test as above.
  5. When the test is complete, close test cocks and remove the hose. Leave
    gate valves A and G in their proper position.
                                                                     31

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          Chapter 6.  ADMINISTRATION OF A CROSS-
               CONNECTION CONTROL PROGRAM

Responsibility
  Public health personnel, waterworks officials, plumbing inspectors, building
managers, plumbing installers, and maintenance men all share to some degree
the responsibility for protecting the  health and safety of individuals  and the
public from  contaminated  water.  These responsibilities  include  insuring
sanitary design and installation practices in piping systems and the supervision
of the installation and maintenance of these  systems. Public health  officials
should promote  the development of sanitary design of plumbing systems and
encourage as well as  assist in  the training of persons responsible for their
installation  and  maintenance.  Officials  responsible  for the  inspection of
plumbing  installations  should  require  the  maximum  protection  against
backflow  that is consistent with  good judgment  and the public safety.
Plumbing  installers  and maintenance personnel should observe and avoid or
eliminate possibilities for backflow and be diligent in adherence to plumbing
codes and ordinances.
  Where  plumbing defects are  detected, notification of the  persons having
authority for the correction of such defects should be  made in writing, and the
responsible  person  should cause these defects to be corrected as  soon as
possible.

Public Water Supply Protection
  Waterworks officials should  survey  their  own and  their  customers'
distribution  systems for cross-connections on a continuing basis and should
provide a  satisfactory program for  the elimination   of  health hazards.
Frequently,  their responsibility  ends at the  property line  but in  some
municipalities it  extends to  the  building piping. Waterworks officials often
prescribe the installation of a backflow prevention device in the service line to
a premise where hazardous use of water is found. The requirement of an airgap
in the service line to  a premise where  extreme hazard is possible  may be
warranted. Reduced pressure  principle or double check-double gate backflow
preventers are often used in cases of lesser hazard.
  Direct connections between potable  and nonpotable water  supply  systems
should be eliminated or properly protected, and interconnections with other
public water supply systems  should be permitted only with the approval of
health authorities.  Private wells should have no connection to the potable,
public water supply system.
  The potable water distribution system should be so designed that the sizes of
pipes are adequate to supply water in the amounts and at the pressures needed.

32

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When a system is sized to meet the needs of peak fire demand, other uses are
usually  covered, but at the time of large fires water pressure in remote parts of
the system may be reduced even to the point of vacuum. Following a large fire,
water and health authorities should be alert for appearances of contamination.
  When there  are main breaks due  to deterioration or  damage, such as by
flood, large  quantities of water escape at the affected  point and pressures
elsewhere  in the system may drop seriously. Breaks  should  be  repaired
promptly and an alert maintained for  the appearance of contamination. The
precaution of first thoroughly flushing, then disinfecting repaired and new pipe
sections should be observed.

Priority of Action

  Plumbing defects are in existence and defects are constantly being created in
new plumbing systems and in altering existing systems. The elimination of
these health hazards will   be possible  only  through  a  well-planned and
continuing program of instruction, plumbing surveillance, and repaid. Many
types of cross-connections exist, and the danger to public health resulting from
each differs widely. The possibility of causing serious pollution of the potable
water  supply  system is  dependent upon the  degree of  hazard  of the
contaminant and the probability of reversed flow.
  Although,  statistically, the probability of reversed flow may seem remote,
reliance should not be placed upon this factor. Complete removal of all cross-
connections  should  be undertaken in an organized  manner  and a priority
system  based upon the degree of hazard involved should be established. It is
not feasible in this manual to assign priority to  all  types of cross-connections,
or even to  classify  them, except in a general  way. Determining priority of
action  in their removal  should be  based primarily on  the nature of the
pollutant.  High priority  should be  given  any  cross-connection  between a
potable water supply and a  piping system or reservoir conveying or containing
sewage,  toxic or  hazardous chemicals, or  nonpotable  water.  All  such
connections should be broken immediately and properly protected.
  Obsolete fixtures, such as tubs and lavatories having inlets terminating below
the overflow level, have a lower priority but outlets should be raised or the
fixtures replaced. Fixtures which  have serrated or  threaded inlets that would
permit  the   extension of these inlets  below  the flood level rim could be
particularly hazardous and should be provided  with vacuum breakers. Where
this is not possible, the fixtures should be replaced on a systematic, improve-
ment basis.  Fixtures  that can siphon only a small amount of relatively  low-
hazard waste water do not warrant urgent or drastic action and can be given a
lower priority. These illustrations describe the common extremes of urgency or
priority, and only a careful evaluation of the circumstances surrounding each
specific  plumbing hazard  will enable  establishing reasonable  priority for
intermediate situations.  As  stated previously,  in establishing a priority of
action,  reliance should  not  be placed upon  the  probability factor of the
occurrence of reversed flow.

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 Method of Action
  A broad program of cross-connection  control should include instruction,
 inspection, improvements, and enforcement.  Control  on  new  installations
 should  be  accomplished through plan review and installation  inspection.
 Control and elimination of existing hazards  should be accomplished through
 routine inspection and periodic surveys at definite intervals. Trained personnel,
 competent in plan examination and hazard  evaluation, should supervise the
 control program.  Sanitary inspectors who have  qualifications equivalent to
 licensed plumbers and who  have been specially trained in cross-connection
 control should be assigned to the task of inspecting new and existing plumbing
 installations.  The results of  periodic  surveys  should  be  tabulated and
 summarized for comparison with the results of previous surveys. Only through
 this means will improvement, or lack of improvement, be noted. Through a
 summarization of the  number of violations of specific types, effective action
 may be directed against the most prevalent and most hazardous violations.
  As an aid to the less-experienced inspector, a limited tabulation of typical
 hazardous  connections  is listed in the appendix of this manual  along with
 several  illustrations  of backsiphonage  and  backflow.  Also shown in the
 appendix is a survey form for reporting on inspections for health hazards.
34

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           Chapter 7.   CROSS-CONNECTION CONTROL
                     ORDINANCE PROVISIONS


                            INTRODUCTION

  The successful  promotion of a cross-connection and backflow-connection
 control program in a  municipality will be dependent upon legal authority to
 conduct such a program. Where a community has adopted a modern plumbing
 code, such as the  National Plumbing Code, ASA A40.8-1955, or subsequent
 revisions thereof,  provisions  of the code will  govern backflow  and cross-
 connections.  It then  remains to provide an ordinance that  will  establish a
 program of inspection for an elimination of cross- and backflow connections
 within the  community. Frequently authority for such a program may already
 be  possessed  by the water department or water authority. In such cases no
 further document may be needed. A cross-connection control ordinance should
 have at least three basic parts.

    1. Authority for establishment of a program.
    2. The technical provisions relating to eliminating backflow and  cross-
      connections.
    3. Penalty provisions for violations.

 The following simple form  is suggested for municipalities who desire to adopt a
 cross-connection control ordinance. The technical provisions are for the most
 part excerpted from a revision of the National Plumbing Code prepared by the
 Public Health Service Technical Committee on  Plumbing Standards (1962).
 Where the  National Plumbing Code, or subsequent revisions thereof, is in
 effect, the technical sections of the following can be replaced by a statement of
 reference to the Code. Communities adopting ordinances should check with
 State  health officials to assure conforrhance with State codes. The form of the
 ordinance should comply with local legal requirements.

           ORDINANCE FOR THE CONTROL OF BACKFLOW
                      AND CROSS-CONNECTIONS

 Section 1.  Authority
  1.1   Responsibility  of  the  Director.  The Director,  Department
of.	, or his designated agent, shall inspect the plumbing in
every  building or premises  in this City as frequently as in his judgment may be
necessary to ensure that such plumbing has been  installed in such a manner as
to prevent the possibility of pollution of the water supply of the city by  the
plumbing. The director shall notify or cause to be notified in writing the owner

                                                                    35

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  or authorized agent of the owner of any such building or premises, to correct,
  within a reasonable time set by the Director, any plumbing installed or existing
  contrary to or in violation of this ordinance, and which in his judgment, may,
  therefore, permit the pollution of the city water supply, or otherwise adversely
  affect the public health.
   1.2  Inspection.  The  Director, or his designated agent, shall have the right
  of entry into  any building, during reasonable hours, for the purpose of making
  inspection of  the plumbing systems installed in such building or premises pro-
  vided that with respect to the inspection of any single family dwelling, consent
  to such inspection  shall  first be obtained from a person of suitable age and
  discretion therein or in control thereof.
  Section 2.  Definitions
    2.1 Agency.  The department of the municipal government invested with
, the authority  and responsibility for the enactment and  enforcement of this
 ordinance.
    2.2 Airgap.  The  unobstructed vertical distance through the free atmos-
 phere between the lowest opening from any pipe or faucet supplying water to
 a tank, plumbing fixture, or other device and the flood-level rim of the recep-
 tacle.
    2.3 Approved.  Accepted by the  agency as meeting an  applicable specifi-
 cation stated or cited in this ordinance, or as suitable for the proposed use.
    2.4 Auxiliary Supply.  Any water source or system other than the potable
 water supply that may be available in the building or premises.
    2.5 Back/low.   The flow of water or other liquids, mixtures, or substances
 into  the distributing pipes  of a potable supply of water from any source or
 sources other than its intended source. Backsiphonage  is one type of backflow.
    2.6 Backflow Preventer.  A device or means to prevent backflow.
    2.7 Backsiphonage.   Backflow resulting  from  negative pressures in the
 distributing pipes of a potable water supply.
    2.8 Barometric  Loop.  A loop of pipe rising at least 35 feet, at i(ts topmost
 point, above the highest fixture it supplies.
    2.9  Check Valve.  A self-closing  device which is  designed to permit the
 flow of fluids in one direction and to close if there is a  reversal of flow.
   2.10  Contamination.  See Pollution.
   2.11  Cross-Connection.  Any physical connection between a potable water
 supply and any waste  pipe,  soil pipe, sewer, drain, or any unapproved source or
 system. Furthermore, it is any potable water supply outlet which is submerged
 or can be submerged in waste water and/or any other source  of contamination.
 See Backflow and Backsiphonage.
   2.12 Drain. Any pipe that carries waste  water or waterborne wastes in a
 building drainage system.
   2.13  Fixture,  Plumbing.   Installed  receptacles,   devices,  or  appliances
 supplied with  water or that receive or discharge liquids or liquid-borne wastes
   2.14  Flood-Level Rim.  The edge of the receptacle from which water over-
 flows.

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  2.15  Hazard,  Health.  Any conditions, devices, or practices in the water
supply  system and  its operation which create, or, in the judgment of the
Director,  may  create, a danger to the health and well-being of the water con-
sumer.  An example  of a health hazard is a structural defect in the water supply
system, whether of  location, design, or  construction,  that regularly or occa-
sionally may prevent satisfactory purification of the water supply or cause it to
be polluted from extraneous sources.
  2.16  Hazard,  Plumbing.   Any arrangement  of  plumbing including piping
and fixtures whereby a cross-connection is created.
  2.17  Hydro pneumatic  Tank.  A  pressure vessel in which air pressure acts
upon the surface of the water  contained  within the vessel, pressurizing the
water distribution piping connected to the vessel.
  2.18  Inlet.  The  open end of the  water  supply pipe through which the
water is discharged into the plumbing fixture.
  2.19  Plumbing System.  Includes the water supply and distribution pipes,
plumbing fixtures, and traps; soil, waste, and vent pipes; building drains and
building sewers including their respective connections, devices, and appurte-
nances  within'the property lines of  the premises; and water-treating or water-
using equipment.
  2.20  Pollution.  The presence of any  foreign substance (organic, inorganic,
radiological,  or biological) in water that tends to degrade its quality so as to
constitute a hazard or impair the  usefulness of the water.
  2.21  Reduced Pressure Principle  Back/low Preventer.  An assembly of dif-
ferential valves and check  valves including an automatically opened spillage
port to  the atmosphere  designed to prevent backflow.
  2.22  Surge  Tank. The receiving,  nonpressure  vessel forming part of the
airgap separation between a potable and an auxiliary supply.
  2.23  Vacuum.  Any pressure less than that exerted by the atmosphere.
  2.24  Vacuum Breaker, Nonpressure Type.  A vacuum breaker designed so
as not to be subjected to static line pressure.
  2.25  Vacuum  Breaker, Pressure  Type. A  vacuum breaker designed  to
operate under conditions of static line pressure.
  2.26  Water, Potable.  Water free from impurities in amounts sufficient to
cause disease or harmful physiological effects. Its bacteriological and chemical
quality  shall  conform  to the requirements  of the Federal Drinking Water
Standards  or  to Ihe  regulations  of the  public health authority  having
jurisdiction.
  2.27  Water, Nonpotable.  Water  that  is not safe  for human consumption
or that is of questionable potability.

Section 3.  General (Technical) Requirements
  3.1  General.  A potable water supply system shall be designed, installed,
and maintained in such manner as to prevent contamination from nonpotable
liquids, solids,  or gases from being  introduced into the potable water supply
through cross-connections or any other piping connections to the sytem.

                                                                       37

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  3.2   Cross-Connections Prohibited.  Cross-connections  between  potable
water systems and other systems or equipment containing water or other sub-
stances of unknown or questionable safety are prohibited  except when and
where, as  approved by the authority having jurisdiction, suitable protective
devices such as the reduced  pressure zone backflow preventer or equal are
installed, tested, and maintained to insure proper operation on a continuing
basis.
  3.3  Interconnections.  Interconnection between two or more public water
supplies shall be permitted only with the approval of the health authority
having jurisdiction.
  3.4  Individual Water Supplies.  Cross-connections between an individual
water supply and a potable public supply shall not be made unless specifically
approved by the health authority having jurisdiction.
  3.5  Connections to Boilers.  Potable water connections to boilers shall be
made through an airgap or provided with an approved backflow preventer.
  3.6  Prohibited Connections to Fixtures and Equipment.  Connection to the
potable water supply system for the following is prohibited unless protected
against backflow in accordance with section 3.8 or as set out herein.
    (a)  Bidets.
    (b)  Operating,  dissection,  embalming, and  mortuary  tables or similar
equipment: in such installation the hose used for water supply shall terminate
at least 12 inches away from every point of the table or attachments.
    (c)  Pumps for nonpotable water, chemicals, or other substances: priming
connections may be made only through an airgap.
    (d) Building drainage, sewer, or vent systems.
    (e)  Any other fixture of similar hazard.
  3.7 Refrigerating Unit  Condensers and Cooling Jackets.  Except where pot-
able water provided for a refrigerator condenser or cooling jacket is entirely
outside the piping or tank containing a toxic refrigerant, the inlet connection
shall be provided with  an approved check valve. Also adjacent to and at the
outlet side of the check valve, an approved pressure relief valve set to relieve at
5 psi above the maximum water pressure at the point of installation shall be
provided if the refrigeration units contain more than 20 pounds of refrigerants.
  3.8 Protection Against Backflow and Backsiphonage.
  3.81   Water Outlets.  A potable water system  shall be  protected  against
backflow and backsiphonage by providing and maintaining at each outlet:
    (a)  Airgap.  An airgap, as specified in section 3.82, between the potable
water outlet  and the flood level rim of the fixture it supplies or between the
outlet and any other source of contamination, or
    (b)  Backflow Preventer.   A device or means to prevent backflow.
  3.82  Minimum Required Airgap.
    (a)  How Measured.  The minimum required airgap shall be measured ver-
tically from the lowest end of a potable water outlet to the flood rim or line of
the fixture or receptacle into which it discharges.
    (b)  Size. The  minimum  required airgap shall  be  twice the effective
opening of a  potable water outlet unless the outlet is a distance less than three

38

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times  the effective  opening away from a wall or similar vertical surface, in
which cases the  minimum required airgap shall be three times the effective
opening of the outlet. In no case shall  the minimum required airgap be less
than shown in table 3.82.
         TABLE 3.82.—Minimum airgaps for generally used plumbing fixtures

Fixture
Lavatories and other fixtures with effective openings
not greater than Vi-in. diameter 	
Sink, laundry trays, goose-neck bath faucets and other
fixtures with effective openings not greater than %-in.
diameter 	
Over rim bath fillers and other fixtures with effective
openings not greater than 1-in. diameter 	
Drinking water fountains— single orifice 7/16 (0.437) in.
diameter or multiple orifices having total area of
0.150 sq. in. (area of circle 7/16-in. diameter) ....
Effective openings greater than 1 inch 	
Minimum
When not
affected by
near walli
(inches)
1.0
1.5
2.0
1.0
(3)
airgap
When
affected by
near wall2
(inches)
1.50
2.25
3.0
1.50
(4)
  1  Side walls, ribs, or similar obstructions do not affect airgaps when spaced from inside
edge of spout opening a distance greater than 3 times the diameter of the effective opening
for  a single wall, or a distance greater than 4 times the diameter of the effective opening
for  2 intersecting walls.
  2  Vertical walls, ribs, or similar obstructions extending from the water surface to or
above the horizontal plane of the spout opening require a greater airgap when spaced
closer to the nearest inside edge of  spout opening than specified in note 1 above. The
effect of 3 or more such vertical walls or ribs has not been determined. In such cases, the
airgap shall be measured from the top of the wall.
  3  2 times diameter of effective opening.
  4  3 times diameter of effective opening.

  3.83  Approval  of  Devices.  Before  any  device  for   the  prevention  of
backflow or backsiphonage is installed, it shall have first been certified by a
recognized  testing laboratory acceptable  to the agency Director.  Devices
installed in a building potable water supply distribution system for protection
against backflow shall be maintained in good working condition by the person
or persons responsible for the maintenance of the system.
  The agency Director or his designee shall inspect routinely such devices and
if found to be defective or inoperative shall require the replacement thereof.

  3.84  Installation of Devices.
    (a)  Vacuum Breakers.  Vacuum  breakers  shall  be  installed with  the
critical level at least 6 inches above the flood level rim of the fixture they serve
and on the  discharge side of the last control valve to  the  fixture. No shutoff
valve or faucet shall be installed beyond the vacuum breaker. For closed equip-
ment or vessels such as pressure  sterilizers the top of the vessel shall be treated
as the flood level rim but a check valve shall  be installed on the discharge side
of the vacuum breaker.
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     (b)  Reduced Pressure Principle Back/low Preventer.  A reduced pressure
 principle type backflow preventer may be installed subject to full static pres-
 sure.
     (c)  Devices  of All  Types.  Backflow  and backsiphonage preventing
 devices shall be accessibly located preferably in the same room with the fixture
 they serve. Installation  in utility or service spaces, provided they are readily
 accessible, is also permitted.


   3.85  Tanks and Vats-Below Rim. Supply.
     (a)  Where a potable water outlet terminates below the rim of a tank or
 vat and the tank or vat  has an overflow of diameter not less than given in table
 3.85, the overflow pipe shall be provided with an airgap as close to the tank as
 possible.

            TABLE 3.85.—Sizes of overflow pipes for water supply tanks
Maximum capacity of water
supply line to tank
0— SOgpm 	
50-150 gpm 	
100-200 gpm 	
200-400 gpm 	

Diameter of
overflow
pipe (inches
ID)
2
2'/2
3
4

Maximum capacity of water
supply line to tank
400—700 gpm
700—1 000 gpm
Over 1,000 gpm


Diameter of
overflow
pipe (inches
ID)
5
5
3


    (b)  The potable water outlet to the tank or vat shall terminate a distance
not less than 1/2 times the height to which water can rise in the tank above the
top of the overflow. This level shall be established at the maximum flow rate of
the supply to the tank or vat and with all outlets except the airgap overflow
outlet closed.
    (c)  The distance from the outlet to the high water level shall be measured
from  the critical point of the potable water supply outlet.
  3.86  Protective Devices  Required.  Approved  devices  to  protect  against
backflow and backsiphonage shall be installed at  all fixtures and equipment
where backflow and/or backsiphonage may occur and where a minimum airgap
cannot be provided between the water outlet to the fixture or equipment and
its flood-level rim.
    (a)  Connections Not Subject to Backpressure. Where a water connection is
not subject to backpressure, a vacuum breaker shall be installed on the dis-
charge side of the last valve on the line serving the  fixture or equipment. A list
of some conditions requiring  protective devices of this kind is given in table
3.86A, "Cross-Connections Where  Protective Devices are Required and Critical
Level (C-L) Settings for Vacuum Breakers."
40

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   TABLE 3.86A.—Cross-connections where protective devices are required and critical
                     level (C—L) settings for vacuum breakers "
     Fixture or equipment
             Method of installation
Aspirators and ejectors

Dental units  .      	

Dishwashing machines . .  .

Flushometers ( closet & urinal)
Garbage can cleaning machine

Hose outlets     	
Laundry machines  ...

Lawn sprinklers	
Steam tables
Tank and vats
Trough urinals
Flush tanks
Hose bibbs (where aspirators or
  ejectors could be connected).
C—L at least 6  in. above flood level of receptacle
 served.
On models without built-in vacuum  breakers—
 C—L  at least 6 in. above flood level rim of bowl.
C—L at least 6  in. above flood level of machine.
 Install on both hot and cold water supply line.
C—L at least 6 in. above top of fixture supplies.
C—L at least 6  in. above flood level of machine.
 Install on both hot and cold water supply lines.
C—L at least 6 in. above highest point on hose line.
C—L at least 6  in. above flood level of machine.
 Install on both hot and cold water supply lines.
C—L at least 12 in. above highest sprinkler or dis-
 charge outlet.
C—L at least 6 in. above flood level.
C—L at least 6 in. above flood level rim or line.
C—L at least 30 in. above perforated flush pipe.
Equip  with approved ball cock. Where ball cocks
 touch tank water equip with vacuum breaker at
 least  1 in. above overflow outlets. Where  ball
 cock  does not touch tank water install ball cock
 outlet at least 1 in. above overflow outlet or pro-
 vide vacuum breaker as specified  above.
C—L at least 6  in. above flood level of receptacle
 served.
 "Critical level (C-L) is defined as the level to which the vacuum breaker may be sub-
merged  before backflow will occur. Where the C-L is not shown on the preventer, the
bottom of the device shall be taken as the C-L.
    (b)  Connections Subject to Backpressure.  Where a potable water con-
nection  is made to a line, fixture, tank, vat, pump, or other equipment with a
hazard of backflow or backsiphonage where the water connection is subject to
backpressure, and an airgap cannot be installed, the Director may require the
use of an approved reduced pressure principle backflow preventer. A partial list
of such connections is shown in table 3.86B.
  TABLE 3.86B.—Partial list of cross-connections which may be subject to backpressure
  Chemical lines
  Dock water outlets
  Individual water supplies
  Industrial process water lines
  Pressure tanks
      Pumps
      Steam lines
      Swimming pools
      Tank and vats—bottom inlets
      Hose bibbs
  3.87  Barometric Loop.  Water connections where  an actual or  potential
backsiphonage hazard exists may in lieu of devices specified in section 3.86 be
                                                                             41

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 provided with a barometric loop. Barometric loops shall precede the point of
 connection.
  3.88  Double  Check-Double Gate Valves.  The Director may authorize in-
 stallation of approved, double check-double gate valve assemblies with test
 cocks as protective devices against backflow in connections between a potable
 water  system and other fluid systems  which present no significant  health
 hazard in the judgment of the Director.
  3.89  Low Pressure Cutoff Required on Booster Pumps.  When  a booster
 pump is used on a water pressure booster system and the possibility exists that
 a positive pressure of 10 psi or less may occur on the suction side of the  pump,
 there shall be installed a low-pressure cutoff on the booster pump to prevent
 the creation of a vacuum or negative pressure on the suction side of the  pump,
 thus cutting off water to other outlets.
 Section 4.  Maintenance Requirements
  4.1  General Requirements.   It shall be the responsibility of building and
 premise owners to maintain all backflow preventers and vacuum breakers with-
 in the building  or on the premises in good working order and to make no
 piping or other arrangements for the purpose of bypassing backflow devices.
  4.2 Backflow Preventers.  Periodic testing and inspection schedules shall be
 established  by the  Director  for  all backflow preventers and  the interval
 between such testing and inspections and overhauls of each device shall be
 established in accordance with the age and condition of the device. Inspection
 intervals should not  exceed 1  year, and overhaul intervals should not exceed 5
 years. These devices should be inspected frequently after the initial installation
to assure that they have been  installed properly and that debris resulting from
the installation  has  not  interfered with the  functioning of the  device. The
testing procedures  shall be in accordance with the manufacturer's instructions
when approved by  the Director.
 Section 5.  Violations and Penalties
  5.1 Notification  of  Violation.  The Director shall  notify the owner, or
authorized agent of the  owner, of the building or premises in which there is
found a violation of this ordinance, of such violation. The Director  shall set a
reasonable  time for the owner to have the violation removed or corrected.
Upon failure of the owner to  have the defect corrected  by the end  of the
specified time interval the Director may, if in his judgment an imminent health
hazard exists, cause the water service to  the building or premises to be  termi-
nated, and/or recommend such additional fines or penalties to be invoked as
herein may be provided.
  5.2 Fines.  The owner or authorized agent of the owner responsible for the
maintenance of the plumbing systems in the building who knowingly permits a
violation to remain uncorrected after the expiration of time set by the Director
shall, upon conviction thereof by the court, be required to pay a fine  of not
more than $100 for each  vioktion. Each day of failure to comply with the
requirements of the ordinance, after the specified time provided under 5.1
shall constitute a separate violation.

42

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           APPENDIX A-PARTIAL LIST OF PLUMBING HAZARDS
                          Fixtures With Direct Connections
Description
Air conditioning, air washer
Air conditioning, chilled water
Air conditioning, condenser water
Air line
Aspirator, laboratory
Aspirator, medical
Aspirator, weedicide and fertilizer sprayer
Autoclave and sterilizer
Auxiliary system, industrial
Auxiliary system, surface water
Auxiliary system, unapproved well supply
Boiler system
Chemical feeder, pot-type
Chlorinator
Coffee urn
Cooling system
Dishwasher
Fire standpipe or sprinkler system
Fountain, ornamental
Hydraulic equipment
Laboratory equipment
Lubrication, pump bearings
Photostat equipment
Plumber's friend, pneumatic
Pump, pneumatic ejector
Pump, prime line
Pump, water operated ejector
Sewer,  sanitary
Sewer,  storm
Swimming pool
                          Fixtures With Submerged Inlets
Description
Baptismal fount
Bathtub
Bedpan washer, flushing rim
Bidet
Brine tank
Cooling tower
Cuspidor
Drinking fountain
Floor drain, flushing rim
                                                                             43

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Garbage can washer
Ice maker
Laboratory sink, serrated nozzle
Laundry machine
Lavatory
Lawn sprinkler system
Photo laboratory sink
Sewer flushing manhole
Slop sink, flushing rim
Slop sink, threaded supply
Steam table
Urinal, siphon jet blowout
Vegetable peeler
Water closet, flush tank, ball cock
Water closet, flush valve, siphon jet

          APPENDIX B-ILLUSTRATIONS OF BACKSIPHONAGE

  The following pages illustrate  typical plumbing installations  where back-
siphonage is possible.
                      FIGURE 21.  Backsiphonage-case 1.

Backsiphonage — Case 1 (fig. 21)
A. Contact Point: A rubber hose is submerged in a bedpan wash sink.
44

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H. lama's of Rewwil l'km<: ( I) A sterilizer connected to Ihe water supply is allowed to
  cool  without opciiiic; the air vent. As it mols. the pressure within the sealed sterilizer
  drops below atmospheric producing a vacuum which draws the polluted water into the
  sterilizer contaminating its contents. (2) The flushing of several flush valve toilets on a
  lower floor which are connected to an undersized water service  line reduces the pres-
  sure at the water closets to atmospheric producing a reversal of Ihe flow.
(.. Suggi'stvil i.«rre<-;iofi:  The waler connection at Ihe hedpan wash sink and I he .sterilizer
  should he provided with properly installed hackflow preventers.
               nun
     nnnnnn
     nnnnnn
     onnnnn
                   Ku;ilKK 22.  Backriphonage—case 2.

Backsiphonage—Case 2 (fig. 22)
A. I'anlact I'oint: A rubber hose Ls submerged in a laboratory sink.
B. Caute of Reversed ik>ir: Two opposite multistory buildings are connected to Ihe same
   waler main, which often lacks adequate pressure. The building on Ihe right has installed
   a booster pump. When the pressure is inadequate in the main, Ihe building booster
   pump starts pumping, producing a negative pressure  in Ihe main and causing a reversal
   of flow in the opposite building.
(!. SuKgcsli'tl (.orri'rlion: The laboratory sink waler outlet should be provided  with a
   vacuum breaker. The water service line lo the booster pump should be equipped with a
   device to cut off the pump  when pressure approaches a negative head or vacuum.
                                                                      45

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                     FIGURE 23.   Backsiphonage-case 3.

Backsiphonage—Case 3 (fig. 23)
A. Contact Point: A chemical tank has a submerged inlet.
B. Cause of Reversed Flow: The  plant fire pump draws suction directly from  the city
   water supply line which  is insufficient  to serve normal plant requirements and a major
   fire at the same time. During a fire emergency,  reversed flow may occur within the
   plant.
C. Suggested Correction: The water service to  the chemical  tank  should  be provided
   through an airgap.

Backsiphonage—Case 4 (fig. 24)
A. Contact Point: The water supply  to  the  dishwasher is not protected by a vacuum
   breaker. Also, the dishwasher has a solid waste connection to the sewer.
B. Cause of Reversed Flow: The undersized main serving the building  is subject to reduced
   pressures, and therefore  only the first  two  floors of the building are supplied dinrtly
   with city pressure. The upper floors are served from a booster pump drawing suction
   directly from the water  service line. During periods of low city pressure, the booster
   pump suction creates negative pressures in  the low system, thereby reversing the flow.
C. Suggested Correction: The dishwasher  hot and cold water should  be supplied through
   an airgap and the waste from the dishwasher should discharge  through an indirect
   waste. The booster pump should be equipped with a low-pressure cutoff device.

Backsiphonage—Case 5 (fig. 25)
A. Contact Point: The gasoline storage  tank is  maintained full and  under pressure  by
   means of a direct connection to the city water distribution system.
B. Cause of Reversed Flow: Gasoline may enter the distribution system by gravity or by
   siphonage in the event of a leak or break in the water main.
C. Suggested Correction:  A reduced  pressure  principle backflow preventer should be  in-
   stalled in the line to the gasoline storage  tank or  a surge tank and pump should be
   provided in mat line.
46

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Main
          r    n    d
          n   n    [
                             n    n   n
~\    n    n
      n
              FIGURE 24.  Backsiphonage-case 4.
              FIGURE 25.  Backsiphonage—case 5.
                                                             47

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                    FIGURE 26.   Backsiphonage-case 6.

Backsiphonage— Case 6 (fig. 26)

A. Contact Point: There is a submerged inlet in the second floor bathtub.
B. Cause of Reversed Flow:  An automobile breaks a nearby fire hydrant causing a rush of
  water and a negative pressure in the service line to the house, sucking dirty water out of
  the bathtub.
C. Suggested Correction: The hot and cold water inlets to the bathtub should be above the
  rim of the tub.

              APPENDIX C-ILLUSTRATIONS OF BACKFLOW

  The following  pages present  illustrations  of typical  plumbing installations where back-
flow resulting from backpressure is possible.
                       FIGURE 27.   Backflow  case 1.
48

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Backflow-Case 1 (fig. 27)
A. Contact Point: A direct connection from the city supply to the boiler exists as a safety
   measure and for filling the system. The boiler water system is chemically treated for
   scale prevention and corrosion control.
B. Cause of Reversed How: The boiler water recirculation pump discharge  pressure or
   backpressure from the boiler exceeds the city water pressure and the chemically treated
   water is pumped into the domestic system through an open or leaky valve.
C. Suggested Correction: As minimum protection two check valves in series should be
   provided in the makeup watcrline to  the boiler system. An airgap separation or reduced
   pressure principle backflow preventer is better.
                         FIGURE 28.   Baokflow-case 2.
Backflow-Case 2 (fig. 28)
A. Contact Point:  Sewage  seeping from a  residential cesspool pollutes the private well
   which is used for lawn sprinkling. The domestic water system, which is served from a
   city main, is connected  to  the  well  supply by  means of a valve. The  purpose of the
   connection may be to prime the well supply for emergency domestic use.
B. Cause of Reversed How: During periods of low city water pressure, possibly when lawn
   sprinkling is at its peak,  the well pump discharge pressure exceeds that of the city main
   and well water is pumped into the city supply through an open or leaky valve.
C. Suggested Correction: The connection between the well water and city water  should be
   broken.
Backflow-Case 3 (fig. 29)
A. Contact Point:  A  valve connection  exists  between the potable and the nonpotable
   systems aboard the ship.
B. Cause of Reversed  Flow: While the ship  is connected to the city water supply system
   for  the purpose of taking  on water for the potable system, the valve  between the
   potable and  nonpotable systems  is opened, permitting contaminated  water to  be
   pumped into the municipal supply.
t  Suggested Correction: Each  pier water outlet should  be  protected against backflow.
   The main water service  to  the pier should  also be protected against backflow by  an
   airgap or reduced pressure principle backflow preventer.

                                                                                49

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City  Main
                                                   •••
                                      To Potable System,
                         FIGURE 29.  Backflow-case 3.

 Backflow-Case 4 (fig. 30)
 A. Contact Point: A  single-valved connection exists between the public, potable water
   supply and the fire-sprinkler system of a mill.
 B. Cause of Reversed  flow: The sprinkler system is normally supplied from a nearby lake
   through a high-pressure pump. About the lake are large numbers of overflowing septic
   tanks.  When  the valve  is left open,  contaminated lake water can be pumped to the
   public supply.
 C. Suggested Correction: The potable water supply to the fire system should be through
   an airgap or a reduced pressure principle backflow preventer should be used.
                    ACME WOOLEN MILLS  |



J

j A
F,A^

Sprinkler System
i
I

M
I
                         FIGURE 30.   Backflow  case 4.
 50

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              APPENDIX D-ILLUSTRATIONS OF AIRGAPS


 The following illustrations describe methods of providing an airgap discharge to a waste
line which may be occasionally or continuously subject to backpressure.
                               Force Main
      FlGl'RE 31.  Airgap to sewer subject to backpressure—force main.
       2XD
                             Indirect Waste
                                                  Ball-Check

                                                        Support Vanes
      Horizontal  Waste

                           Gravity Drain


     FIGURE 32.   Airgap to sewer subject to backpressure—gravity drain.
                                                                      51

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  Nonpotable Supply
Potable Supply
    FIGURE 33.  Fire system makeup tank for a dual water system.
     APPENDIX E-ILLUSTRATIONS OF VACUUM BREAKERS
                                         Vacuum Closes Gate
                                Air Enters
                                Here Pre-
                                venting Rise
                                of Contamin
                                ated  Liquids
                                in Fixtures
     Flush
  Connection
 Cowl  Nut
                        Air Vent
                                                  B
                   FIGURE 34.  Vacuum breakers.
52

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NOTE:

  (T)'/2"  or  %" Gate Valve


  (Y)'/2"  or  %" Sch. 40. Galv.


  (3)'/2"  or  %" Vacuum Breaker

  (T)'/2"  %" EM. M.  I.  Galv.

  MHExterior  Building  Wall

  (T)l" Sleeve, Sch. 40

  (7J Handwheel

  MMlPS  Hose  Adapter

  MnCoupling M. I.  Galv.

  (ToV/2"  °f  %" Nipple
Plan
                                                 Section  "A""A"
    FIGURE 35. Vacuum breaker arrangement for an outside hose hydrant.
    (By permission  of Mr. Gustave J. Angele ST., P.E.  Formerly  Plant Sanitary
    Engineer, Union Carbide Nuclear Division, Oak Ridge, Tenn.)

                         APPENDIX F-GLOSSARY

Air gap
  The unobstructed  vertical distance through the free atmosphere  between the lowest
opening from any pipe or  faucet supplying water to a tank, plumbing fixture, or other
device and the flood-level rim of the receptacle.
Backflow
  The flow of water  or other liquids, mixtures, or substances into the  distributing pipes of
a potable  supply of water  from any source or sources other than its intended source.
Backsiphonage is one type of backflow.
Backflow Connection
  Any arrangement whereby backflow can occur.
Backflow Preventer
  A device or means to prevent backflow.
                                                                           53

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Backflow Preventer, Reduced Pressure Principle Type
  An assembly of differential valves and check valves including an automatically opened
spillage port to the atmosphere.
Backsiphonage
  Backflow resulting from negative pressures in the distributing pipes of a potable water
supply.
Cross- Connection
  Any physical connection  or  arrangement  between  two  otherwise separate piping
systems, one  of  which contains potable water, and the other,  water of unknown or
questionable safety, or steam, gases, or chemicals, whereby there may be a flow from one
system to the other. No physical cross-connection should be permitted between public or
private water  distribution  systems  containing  potable water  and any other system
containing  water  of questionable  quality  or  containing contaminating or polluting
substances.

Effective Opening
  The minimum cross-sectional area at the point of water supply discharge, measured or
expressed in terms of (1) diameter of a  circle, or (2) if the  opening is not circular, the
diameter of a circle of equivalent  cross-sectional area.
Flood-Level Rim
  The edge of the receptacle from which water overflows.
Flushometer Valve
  A  device  which  discharges a predetermined quantity of water to fixtures for flushing
purposes and is actuated by direct water pressure.
Free Water Surface
  A water surface that is at atmospheric pressure.
Frostproof Closet
  A  hopper with no water in the bowl and with the  trap and water supply control valve
located below frost line.
Indirect  Waste Pipe
  A  drain  pipe used  to convey  liquid wastes that  does not connect directly with the
drainage system, but which  discharges into the drainage system through an airbreak into a
vented trap or a properly vented and trapped fixture, receptacle, or interceptor.
Plumbing
  The practice, materials, and fixtures used in the installation, maintenance, extension, and
alteration of all piping, fixtures, appliances, and appurtenances in connection with any of
the following:  sanitary drainage  or  storm drainage facilities,  the venting system and the
public or private water-supply systems, within or adjacent to any building, structure, or
conveyance; also  the  practice  and  materials used in the installation,  maintenance,
extension,  or alteration of  storm water, liquid  waste,  or sewerage,  and water-supply
systems of any premises to their connection with any point of public  disposal or other
acceptable terminal.
Potable Water
  Water free from impurities  present in amounts sufficient to cause disease or  harmful
physiological effects. Its bacteriological and chemical quality shall conform to the require-
ments of the Public Health Service Drinking Water  Standards  or the regulation of the
public health authority having jurisdiction.
Vacuum
  Any absolute pressure less than that exerted by the atmosphere.

54

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 Vacuum Breaker
  A device that permits air into a water supply distribution line to prevent backsiphonage.
 Water Outlet
  A discharge opening through which water is supplied to a fixture, into the atmosphere
(except into an open tank which is part of the water supply system), to a boiler or heating
system, to any devices or equipment requiring water to operate but which are not part of
the plumbing system.
Water Supply System
  The water service pipe, the water-distributing pipes, and the necessary connecting pipes,
fittings, control  valves,  and all appurtenances in or adjacent to the building or premises.
The water supply system is part of the plumbing system.

                       APPENDIX G-BIBLIOGRAPHY

A Revision of The  National Plumbing Code, ASA  A40.8-1955, Report of the Public
  Health Service Technical  Committee on  Plumbing Standards.  Sept. 15,  1962, Public
  Health Service, Washington 25, D.C.
Accepted Procedure and Practice in Cross-Connection Control, Pacific Northwest Section,
  American Water Works Association, Oct. 1971.
Angele, Gustave  J., Cross-Connection and Back/low Prevention,  American Water Works
  Association. Supplementary Reading Library Series - No. S106, New York 10016.
Control and Elimination of Cross-Connections, Panel Discussion, Journal American Water
  Works Association, VoL 50, No. 1, 1960.
Cross-Connection Complications, The Capital's Health, Vol. II, No. 9, Dec. 1953, D.C.
  Dept. of Public Health, Washington, D.C.
Dawson, F. M.,  and Kalinske, A.  A., Report on  Cross-Connections and Backsiphonage
  Research, Technical Bulletin No.  1, National Association of Plumbing, Heating, Cooling
  Contractors, Washington, D.C.
How To Prevent Industrial Cross-Connection Dangers,  Water Works Engineering,  Feb.
  1962.
Manual of Cross-Connection Control, Foundation for Cross-Connection Control Research,
  University of Southern California, Los Angeles, Calif. 90007, Mar. 1969.
Regulations Relating  To Cross-Connections,  except from the California Administrative
  Code, Title 17, Public Health, 1956.
Springer, E.  K., and Reynolds, K. C., Definitions and Specifications of Double Check
  Valve Assemblies  and  Reduced Pressure Principle  Backflow  Prevention Devices,
  University of Southern California, School of Engineering Rept. 48-101, Jan. 30,1959.
Taylor, F.  B., and Skodje,  M. T., Cross-Connections, A Hazard in All  Buildings, Modern
  Sanitation and Building Maintenance, Vol. 14, No. 8, Aug. 1962.
Use of Backflow  Preventers for Cross-Connection Control,  Joint Committee Report,
  Journal American Water Works Association, Vol. 50, No. 12, Dec. 1958.
Van Meter, R. O., Backflow Prevention Hardware, Water and Wastes Engineering, Pt. 1,
  Sept. 1970; Pt.  2, Oct.  1970.
                                                                              55

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                               APPENDIX H

                  CROSS-CONNECTION SURVEY FORM

Place:	   Date:.
Location:		   Investigator(s):.
Building Representative(s) and Title(s):
WaterSource(s):-
Piping System(s):-
Points of Interconnection:
Special Equipment Supplied with Water & Source:
Remarks or Recommendations:.
 NOTE:  Attach  sketches of cross-connections found where necessary for clarity  of
description. Attach additional sheets for room by room survey under headings

    Room Number                                         _ Description of
                                                          Cross-Connectio n(s)
56

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                                     INDEX
                                    Page
 Administrative Authority  	23, 35
 Airgap	19, 20, 21, 32
 Auxiliary Piping  	  16
 Auxiliary System  	 18, 25
 Backflow  	  9, 15, 1749, 21, 25, 26
                               29, 32, 34
 Backflow Preventers
    Barometric Loop   	  25,26
    Double Check Valve   	  25
    Double Check-Double
       Gate Valve  	  25, 26, 32
    Reduced Pressure
       /one Device  	24, 25, 32
    Single Check Valve  	  25
    Swivel Connection	 25, 26
    Tests  	27-30
    Vacuum Breaker-Non-
       Pressure Type   	 22, 24
    Vacuum Breaker-
       Pressure Type	  22
 Backpressure	16, 18, 21, 22, 24-27
                                  30,31
 Backsiphonage  	9, 15-17, 19, 21, 23
                                  24,34
                                  25, 26
                                 , 20, 21
Barometric Loop   	
Booster Pump  	  15, 18, .'
Check Valves  	  25, 26, 32
Codes and Ordinances	32, 35-42
Connections — Basic Types
   Solid Pipe  	16
   Submerged Inlet-Outlet  	 16, 19
   Valved  	 17
Control Program 	32-34
Color Coding  	 21
Chemical Poisonings
   Arsenic  	 4,  6
   Chromatcs  	 5,  7
   Chlorides  	  5
   Ethylene C.lycol   	6
   Fertilizer  	  8
Cross-Conncction
   Causes  	  1
   Definition  	  1, 9, 54
   Examples	  3-8, 44-50
   Ordinances  	35-42
   Policy, AWWA	  vii
   Prevention	 1,2
   Survey Form   	  56

Effective Opening 	  20

Flood Level Rim	16, 20, 22, 24, 27
                                     33
Inspection and Maintenance 	  18
Interconnections	  21, 32

Pressure
   Absolute  	9, 12
   Atmosphere	9,11, 21, 23, 25, 28
   Differential  	18, 21, 25, 28-30
   Gage   	9, 12
   Negative   	 17,21,23
   Static	12-14
   Water	 10, 16, 21, 27
Pressure  Head  	  10
Pressure-Reducing Valve  	21
Private Wells  	  32
Pump Air Binding 	  21
Reduced Pressure /one
   Backflow Preventer 	 24, 25, 32

Siphon Theory  	11-17
Surge Tank 	  20, 21
Swivel Connection   	25, 26

Tests - Backflow Preventers	27-30

U-Tube   	  13

Vacuum   	9, 21, 26, 33
   Partial 	  12,13
Vacuum  Breaker 	22, 24
Vaporization	  15

Waterborne Diseases
   Amebic Dysentery	 1
   Badllary Dysentery 	4, 5
   Brucellosis	3
   Gastroenteritis	4-7
   Hepatitis  	 7
   Poliomyelitis 	 5
   Shigellosis  	 7
                                                                              57

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